Remote monitoring and control system

ABSTRACT

A system is disclosed which is capable of monitoring the condition of an apparatus, generating signals indicative of that condition, and, at a remote location, providing signals indicative of the detected status. The remote unit comprises a controllable oscillator which produces a signal which may be pulsed, or modulated, to represent data to be sent to the base station. The base unit includes three monitoring circuits responsive to the pulse rate of the data signals to provide positive readings of the status of the device being monitored. The first monitoring circuit represents a rest condition at the remote station when in a first state of energization, and indicates an alarm, or fault, condition when in a second state of energization, for example. In this second state, the second monitoring network is also energized to provide a positive indication of the alarm. The third monitoring circuit is a selfsurveillance circuit which becomes energized when the telemetering network malfunctions. By energizing the monitoring networks in various combinations, additional information concerning the remote station can be derived. Audible alarm means are provided in conjunction with the monitoring networks to indicate a fault condition at the remote unit. Switching means are provided to turn the audible alarm off during the time that the fault condition is being corrected, the alarm again sounding when corrections have been made and the system is ready to be returned to its monitoring condition.

llnited States Patent Leslrer [451 Feb. 8, 1972 [54] REMOTE MONITORINGAND CONTROL SYSTEM [72] Inventor: John C. besher, Erie, Pa

[73] Assignee: James Barber, Erie, Pa. a part interest [22] Filed: Dec.23, 1968 [21] Appl. No.: 786,316

Primary ExaminerThomas B. Habecker Attomey.lones & Lockwood ssuQLCONTROLLED OSCILLATOR CONTROLLER- MODULATOR SENSORS FOR APPARATUS TO BEMONlTORE [57] ABSTRACT A system is disclosed which is capable ofmonitoring the con. dition of an apparatus, generating signalsindicative of that condition, and, at a remote location, providingsignals indicative of the detected status. The remote unit comprises acontrollable oscillator which produces a signal which may be pulsed, ormodulated, to represent data to be sent to the base station. The baseunit includes three monitoring circuits responsive to the pulse rate ofthe data signals to provide positive readings of the status of thedevice being monitored. The first monitoring circuit represents a restcondition at the remote station when in a first state of energization,and indicates an alarm, or fault, condition when in a second state ofenergization, for example. In this second state, the second monitoringnetwork is also energized to provide a positive indication of the alarm.The third monitoring circuit is a self-surveillanoe circuit whichbecomes energized when the telemetering network malfunctions. Byenergizing the monitoring networks in various combinations, additionalinformation conceming the remote station can be derived. Audible alarmmeans are provided in conjunction with the monitoring networks toindicate a fault condition at the remote unit. Switching means areprovided to turn the audible alarm off during the time that the faultcondition is being corrected, the alarm again sounding when correctionshave been made and the system is ready to be returned to its monitoringcondition.

24 Claims, 9 Drawing Figures PATENTEDFEB 8 m2 SHEET '4 OF 5 TO PARALLELUNITS BUZZER 1 l 1 I l l F7616 I I I 1 l l I 2/32 g3! //v v/vr0/? JOHNC. LESHER PATENTEUFEB 8 m2 SHEET 5 OF 5 |ll||i|| WW 303 I nv VEN TORJOHN 6.. LESHER rare/v5 rs REMOTE MONITORING AND CONTROL SYSTEMBACKGROUND OF THE INVENTION The present invention relates, in general,to systems for monitoring, controlling or communicating with remotelylocated circuits or mechanical devicesi more particularly, the inventionrelates to a system for detecting the status of a burglar alarm, firealarm, or the like, and for monitoring. the operation of mechanicaldevices such as machine tools, electric motors, pumps, or the like, andproviding at a base station positive indication of the circuits andstatus so monitored.

Systems for carrying to a base location'signals indicative of the stateor status of remote equipment are, of course, well known, and over theyears large numbers of complex systems have been devised for providingaccurate and reliable indications of remote conditions. The prior arthas become extremely adept at transmitting such information, but invirtually every system thus far devised, a major problem has been thedetection of false signals due to malfunctions in the system. Thesemalfunctions can occur in the remote unit, in the monitoring networks ofthe base unit or in the connections between these units. Where suchamalfunction occurs, it is possible that an alarm or other faultcondition can occur unnoticed with resultant damage to the equipmentbeing monitored, and corresponding serious economic loss is possible.

A further difficulty observed in many prior systems is the requirementfor a power supply at the remote location. Where the remote unit is tobe located at a relatively inaccessible spot, this requirement oftenpresents an insurmountable problem. Further, where the remote locationis in an environment where power supplies can present a hazard, as forexample, in a coal mine where a small spark might cause a dustexplosion, such prior systems cannot be used.

Finally, such systems are often designed for specific uses andapplications, and thus are not suitable for general purposeapplications. n the other hand, where some flexibility is built intoprior systems, their design becomes complex and economic factors preventtheir use, for it is undesirable to use a highly sophisticated system inan application which can be handled by a very simple system, even thoughthe complex arrangement might be capable of providing the requiredfunctron.

SUMMARY OF THE INVENTION It is an object of the present invention toovercome the disadvantages of prior art systems by providing asimplifiedelectronic system which is constructed in a modular form to providegreat flexibility in function-and use.

lt is a further object of the present invention to provide a modularsystem which produces positive indications of system status and whichis' self-surveying to prevent errors due to system malfunction.

Another object of the present invention is to provide a modular systemwhich is capable of reliably monitoring equipment and apparatus locatedremotely from a base station and where the remote portion of the unitdcies not require a power supply.

Briefly, the invention comprises a base unit and a remote unitinterconnected by means of suitable cables or wires which serve to carryoperational power from the base unit to the remote station and whichcarry pulses representative of the status of the device being monitoredfrom the remote station to the base station. In addition to itsmonitoring functions, the system is also capable of providing controlsignals to the remote unit for the purpose of effecting controloperations at the remote station. The system may be used, for example,to respond to remotely located burglar alarms, fire alarms and relatedequipment, to operate and to sense the functioning of remotely locatedmachines such as presses, ventilating systems such as may be used incoal mines, gate or yard controls such as may be used in lumber supplyyards, to monitor and control offshore drilling equipment, oil or gasfuel pumps and equipment, and to provide remote indications of machinetool operations and similar systems which require surveillance and/orcontrol functions.

The remote portion of the system includes an oscillator and means forcontrollably pulsing, or modulating, the oscillator output in responseto sensed conditions. The unit's modular construction permits its usewith a great variety of sensor devices without requiring changes in theoscillator or controller modules. The remote unit is connected to thebase station byway of two lines which serve to carry power from the basestation to the remote unit and, in addition. transmit the oscillatoroutput to the base unit.

The base station consists of three basic indicator modules which serveto monitor the condition being sensed at the remote station and toprovide indications of the sensed condition. Each module carries anindicator lamp for visual monitoring, with an alarm module beingavailable to provide audible' signaling. The first module may beprovided with a green indicator lamp which will respond to the normal,or ready," output of the remote oscillator to provide a blinking signal.This pulsing green light indicates a clear supervised circuit from thebase station to the remote station and indicates to the system operatorthat the connecting wires and components are working properly. This isthe first mode of operation for the present system.

The second mode of operation of thesystem results from a change in theoutput from the remote oscillator. This change produces a steady glowfrom the indicator lamp of the first monitor section and a resultantsteady glow from the second indicator module which may, for example,carry a red indicator lamp. This condition may be indicative of machineoperation, where mechanical motion of some type is to be detected, mayrepresent a burglar or fire alarm, or may represent some other function,depending on the use to which the system is being put. This mode may betermed an active condition of the system.

The third mode of operation occurs in response to a malfunction withinthe system. A malfunction such as a broken or shorted connecting wire ora defective component at the base or remote stations will result inenergization of the third monitoring section. An amber lamp, forexample, may be used to provide a visual indication of the malfunction.

The fourth mode of operation available in the system provides analternate blinking of the green and amber lamps and is indicative of auniqueoutput from the oscillator which may result from a specifiedmachine operation, may indicate the activation of a specific circuitsuch as a burglar alarm, or may be a manually initiated signal to permitcommunication between the remote and base stationsThis mode may betermed a "warning condition.

The final mode which will be described provides a sequential blinking ofall three indicator module lamps to provide a positive indication of aspecified condition at the remote station. Again, this may be responsiveto a manually actuated signal, or one produced by a predeterminedcondition. For convenience, this may be referred to as a signaling"condition. In general, the remote unit may be said to exhibit twoconditions: a ready" condition, and a fault condition, the formeroccurring when the remote unit is operating properly, and the latterwhen the remote oscillator is operating at a frequency other than itsnormal rate. Thus, one of the primary features of the invention lies inits flexibility, which permits indication of a great variety of remoteconditions accurately and reliably, with positive and easily identifiedoutput signals as suring quick response to a fault condition.

The system preferably is completely solid state, with each module beingcomplete in itself. Except for the various switches, the modules areencapsulated in a suitable epoxy compound to withstand fungus, moistureand chemical attack. With proper selection of components, ambienttemperature variations from --40 C. to C. will not affect the electricalstability of the system, thus permitting it to be used in a variety ofapplications and environments. It has been found that silicontransistors provide the required temperature stability. as

well as providing long life and reliability. Through the use ofsolid-state devices, only a relatively small power supply need beprovided. Further, the system is compact and easy to handle, requiringlittle space for installation. A number of central station units may bemounted on a common panel and may share a common power supply. Ifdesired, the audible alarms may be common to several units.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and additional objects,features and advantages of the invention will be seen in the followingdescription of preferred embodiments thereof. The novel features whichare characteristic of the invention are described with particularity inthe appended claims, but for a complete and full understanding of theinvention, reference will now be made to certain specific embodiments,selected for purposes of illustration and shown in the accompanyingdrawings, in which:

FIG. 1 is a block diagram of the monitoring and indicating system of thepresent invention;

FIG. 2 is a more detailed block diagram ofa power supply suitable foruse with the system of FIG. 1;

FIG. 3 is a circuit diagram of the remote station of the invention usedin combination with a burglar or fire alarm system;

FIG. 4 is a circuit diagram of the three base station monitoringnetworks;

FIG. 5 illustrates an audible alarm system suitable for use with theindicator networks of FIG. 4;

FIG. 6 illustrates a machine control circuit for use at the remotestation for controlling and sensing the operation of a suitableoperating mechanism;

FIG. 7 illustrates an alarm network for the base station monitornetworks during a machine controlling operation;

FIG. 8 illustrates a further sensing means which may be superimposed onthe output of the remote station circuitry of FIG. 3 for effectingadditional monitoring operations; and

FIG. 9 is a circuit diagram of a suitable meter for detecting thesignals produced by the circuit of FIG. 8.

DESCRIPTION OF PREFERRED EMBODIMENTS Turning now to a consideration ofthe block diagram illustrated in FIG. 1, it will be seen that thepresent system comprises a remote station 10 and a base station 12interconnected by lines 14 and 16. The interconnecting lines may be anysuitable length, and it has been found that distances of up to 15 milesor more between the remote and base stations may be accommodated by thepresent system. The remote unit comprises an oscillator 18 which iscapable of operating at a plurality of pulse rate levels, but which willprovide a constant output at the selected level. A controller, ormodulator, circuit 20 regulates the pulse rate of oscillator 18 and,although it is illustrated as a separate element in FIG. I, thecontroller may comprise a part of the oscillator module. This controlleroperates in response to inputs from sensors 22, which are responsive tothe apparatus which is to be monitored by the system to pulse modulatethe oscillator and thereby provide an output that is uniquelyrepresentative of a monitored condition. These sensors may include aburglar alarm, fire alarm, or the like, or may be motion sensitivedevices for detecting the operation of a machine of some type. Broadlyspeaking, then, the sensors may be arranged to respond to the status ofa device and will change in a predetermined way when the condition beingmonitored changes; i.e., when a machine that is supposed to be movingstops, when a fire detector which is i supposed to have an open circuitproduces a closed circuit, when a rotating ventilator fan stops turning,etc. This change in the sensor serves to vary the state of thecontroller 20 and thus to change the output pulse rate ofoscillator 18.

The output of oscillator 18 is applied to lines 14 and 16 in the form ofpulses, the pulse rate carrying the desired information from sensors 22.These pulses are superimposed on the direct current power supplied tothe remote station on lines [4 tion. The pulses are applied by way oftransformer 26 to the first monitor network 28, which responds tovarious pulse rates to produce visual indications of the status of theremote equipment. The visible indications are provided by any suitablemeans, but preferably a lamp 30 is used. since the nature of theindications is suited to such a display. The lamp on the first monitormay be a bulb of'some selected color for easy identification; forpurposes of illustration it will be considered to be green. When thetelemetering system is in a normal, or ready" mode, and operatingproperly, the output of oscillator 18 will have a pulse rate which willcause lamp 30 to blink at a moderate pace. A change in the apparatusbeing monitored which results in an increase in the pulse rate oftheoscillator, or which produces an unmodulated, continuous, pulse outputwill cause the green lamp to glow steadily. and in this "active" mode ofoperation a second monitor 32 will respond, providing a visualindication of such a mode on a second indicator lamp 34. This secondlamp may be considered a red lamp for purposes of illustration.Excitation of the second monitor may serve to operate a switch 36 tosound an alarm 38 to give an audible warning of the changed condition,unless this active mode is indicative of a desired event. In this lattercase, the alarm circuit will be modified to respond when this secondmode ends.

As long as the first monitor is receiving pulses in the normal manner, aswitch 40, sensitive to the first monitor, will remain closed; however,a fault in the remote system or in lines 14 and 16 will cut off theinput to the first monitor, permitting switch 40 to open and allowing athird monitor network 42 to become energized. This indicates amalfunction in the system and is made visible by energization of amberlamp 44. This lamp will also indicate a malfunction in either the firstor the second monitor network and further may be used in combinationwith the green or red lamps to indicate a specific condition at theremote location. Thus, a plurality of indicator modules are providedwhich will give positive visual indication of the status not only of acondition or element to be monitored, but ofthe monitoring circuitry aswell.

FIG. 2 is illustrative of a power supply which is useful with the systemof the present invention. Although it will be apparent that the presentsystem can be operated as an alternating current system, it is preferredthat direct current be used, and thus power supply 24 is illustrated asproviding a regulated direct current to the system. An alternatingcurrent source is connected through transfer switch 52 to a conventionalrectifier and regulator circuit 54 which is adapted to provide 44 voltsof regulated direct current. Voltage from regulator 54 is applied acrosslines 14 and 16 for use at the remote station; parallel remote stationsmay be connected to this same source of DC voltage by way of lines 56and 58, if

desired. A switching module 60 may be connected between voltage source54 and lines 14 and 16 in certain embodiments of the invention.Switching module 60 comprises series resistors 62, 64 and 66 and a shuntcapacitor 68 which serves to dampen switching transients. An on-offswitch 70 shunts resistor 66, and operation of this switch serves tovary the current level supplied to lines 14 and 16. The resultingvariation in current level may be used at the remote station to operatea solid-state switching device, in a manner to be described below. Aswill be explained with regard to FIGS. 8 and 9, additional detectingcircuits may be included in the present system. Thus, a probe amplifier72 may be included in line 16, the probe serving to sense apredetermined condition or value, such as fluid flow, and to produce anoutput which, again, is superimposed on the signals normally carried bylines 14 and 16. A meter circuit 74 may be provided to detect the outputfrom the probe amplifier 72.

Direct current is supplied to the base station by way of rectifier andregulator 76 in the power supply network 24. In order to insurecontinuity of operation, a standby source of alternating current may besupplied to transfer switch 52 by way ol'un inverter 78 and a standbybattery supply 80. Such standby supplies are well known in the art, anddo not require further explanation. However, it is noted that since thesystem of the present invention draws only a very small current, abattery standby source is practical.

Turning now to a consideration of the remote unit, FIG. 3 illustratesthe oscillator 18 and the controller module in combination with asurveillance system such as a conventional burglar alarm or firedetectors. The oscillator basicallyconsists-of a unijunction transistorQ1 having its two base electrodes 86 and 88 connected by way of resistor90 to output line 92 and resistor 91 to power supply line 14,respectively. The emitter of unijunction transistor O1 is connected tothe junction of a biasing resistor 93 and a biasing capacitor 94 whichare connected in series between lines 92 and 14. A second capacitor 95is connected in parallel with the series arrangement of resistor 93 andcapacitor 94, and a Zener diode 96 is connected in parallel withcapacitor 95 to limit the voltage appearing across capacitor 95 and toprovide a constant voltage supply on line 92. As is well known inunijunction transistor oscillators, the voltage across capacitor 94gradually builds at a rate determined by the time constant of thebiasing circuit 93, 94, to the point where the transistor 01 becomesconductive. This discharges capacitor 94 through Q1 and produces avoltage drop across load resistor 91, which voltage is applied throughcoupling capacitor 97 to the base of transistor amplifier Q2. TransistorQ2 amplifies the voltage so provided and applies it to line 16 fortransmission to the base unit. Upon completion of the discharge ofcapacitor 94, Q1 stops conducting and capacitor 94 again begins to buildup a charge. The rate at which capacitor 94 charges controls thefrequency at which 01. fires capacitor 94, and thus regulates thefrequency of the signals applied to line 16 through amplifier Q2 underfree-running conditions.

As is known, the frequency of a unijunction oscillator can be varied innumerous ways, as by changing the rate at which the voltage onitsbiasing capacitor builds up to the firing level. It has been found,however, that such changes in oscillator frequency do not always providesatisfactory results where information is to be transmitted with a highdegree of accuracy, for changes in ambient conditions or in componentcharacteristics can affect the signal being transmitted and thus varythe information being transmitted. ln the present case, stepped signalvalues, or discrete pulse rates, are used in order to provide positiveindications of changed conditions. The required pulse rate signals areobtained by means of a pulse rate timing circuit which modulatesoscillator 18, the pulse rate timing circuit using suitable transistorswitches to periodically shunt the firing circuit of the unifunctionoscillator. The pulse rate timing circuit may itself be varied to permitselection of discrete pulse rates for the oscillator output whereby therepetition rate of the output pulses transmits information concerningthe condition of the system or apparatus being monitored. In thismanner, changes in component characteristics due to ambient conditionshave little effect on the transmitted signals.

Selection of the pulse rate output for oscillator O1 is carried out incontroller 20. A transistor switch O3 is connected in series with atiming capacitor 100 between line 14, which may be considered a groundline, and line 101, which is connected to the junction of resistor 93and capacitor 94, and thus is connected to the emitter of Q1. Whentransistor 03 is conductive, it connects capacitor 100 between lines 101and 14, in parallel with capacitor 94. Capacitor 100 is also connectedacross the collector-emitter circuit of a timing transistor Q4 which isin Series with the collector-emitter circuit of transistor 03. Capacitor100 begins to charge when 03 becomes conductive, and when this chargebuilds up to a high enough value, transistor 04 is fired, providing apath from line 101 through 04 and O3 to ground line 14 which shuntscapacitor 94 and prevents 01 from oscillating, as will be describedhereinbelow, and which shunts capacitor 100 to ground to discharge it.04 then is cut off,,capacitor 100 begins to charge, Q1 starts tooscillate again, and the cycle is repeated. The base of O3 is connectedto lines 14 and 92 by way of resistors I02 and I03, respectively, withcapacitor 104 being connected between the base electrode of Q3 and line14, in parallel to resistor 102. The base of O3 is connected by way ofline 105 to terminal 106, for connection to the sensor circuitry ofmodule 22. Similarly, line 14 is connected to terminal 107.

A first surveillance or supervisory, loop may be connected acrossterminals 106 and 107 in the sensor circuit. A break in the portion ofthe surveillance loop connected to terminal 107 would open line 14,whichis the ground return line for the system, and this would produce amalfunction signal at the base station. Detector means such as thoseillustrated at 110 and 111 in sensor 22 may be connected betweenterminals 106 and 107. These detectors may be heat-sensitive devices fora fire-warning system or any suitable conventional detector whichresponds to a specified condition to provide a short circuit. Such ashort circuit created by one or more of the detectors may be termed afault condition, and would shunt resistor 102 and capacitor 104 in thebase of transistor Q3, removing its bias and causing it to cut off. Thiswould remove capacitor 100 and transistor Q4 of the pulse rate timingcircuit from the emitter circuit of oscillator Q1 and would allow 01 tooscillate continuously at its free-running value, as determined bycapacitor 94. Capacitor 100 is shunted by transistor 04, the emitter ofwhich is connected through resistor 112 to the collector of Q3 and thecollector of which is connected to line 101. The base ofQ4 is connectedto line 101 and one side of capacitor through bias resistor 113 and isconnected to terminal 114 for connection to the sensor module 22. Asecond surveillance loop 116 is then connected between terminals 106 and114, and as long as this second surveillance loop remains intact, thebase voltage will be determined by resistors 113 and 102, acting as avoltage divider between lines 14 and 101. The base voltage on.Q4 willthus remain low and conduction of Q4 will be controlled by the voltageacross capacitor.

100, as, will be described. If the second surveillance loop shouldbreak, resistor 102 will be removed from the bias circuit, and the basevoltage applied to Q4 through resistor 113 would be sufficiently high topermit Q4 to conduct, the voltage for this purpose being derived fromline 16 by way of line 92, resistor 93 and line 101. Steady conductionof 04 together with continued conduction of 03 provides a shunt acrossboth capacitors 94 and 100 through resistor 112, preventing thecapacitors from charging, and stopping oscillation of O1 to produce azero pulse rate output. However, even under this condition the systemwould be capable ofresponding to the operation of detectors 110 and 111,for a short circuit in one of these detectors would cut off transistor03, returning the oscillator 01 to its free-running state under thecontrol of capacitor 94 alone. Thus, it will be seen that the firstsurveillance loop, which includes detectors 110 and 111, and the secondsurveillance loop, which includes wire 116, are capable of responding tovarious conditions to modulate the output of oscillator Q1.

With the surveillance loops intact and the detectors open circuited, theremote unit will operate in its normal mode. Thus, transistor 03 isconducting, receiving its base bias from line 92 through resistordivider 103, 102. The voltage on line 92 is applied by way of resistor93 to capacitor 94, causing this capacitor to charge to the firingvoltage for the unijunction transistor Q1, and to capacitor 100, causingthis latter capacitor to charge toward a voltage value which will biastransistor Q4 into conduction. Capacitor 94 charges through resistor 93much more quickly than does capacitor 100, because of the resistance ofthe collector emitter circuit of transistor Q3 in the charging circuitof capacitor 100; therefore capacitor 94 will charge and fire Q1 anumber of times before capacitor 100 reaches its full charge so that Q]will oscillate. When transistor Q4 is biased into conduction by thecharge on capacitor 100, O4 shunts capacitors 94 and 100 to line 14through transistor Q3, stopping the oscillation of Q1 and dischargingboth capacitors through resistor 112 and transistor Q3. Transistor Q4then becomes nonconductive, and the cycle repeats. This cycle ofoperation is termed the pulse rate ofthe circuit.

Two additional control capacitors are illustrated in controller 20, oneof which is indicated as being manually operable and the other of whichis either manually operable or responsive to a sensing mechanism such asa burglar alarm. The first capacitor 119 may be connected in shunt withcapacitor 100 by way ofline 120, which is connected to previouslydescribed line 101, manually operable switch 121, the capacitor 119, andline 122. When transistor O3 is conducting, closure of switch 121 placescapacitor 119 in shunt with capacitor 100 to provide a correspondingchange in the pulse rate of the circuit. In similar manner, the secondcapacitor 125 may be connected in shunt with capacitor 100 by means of amanually operated switch 126, again effecting a distinctive change inthe pulse rate of the circuit.

Capacitors 119 and 125 may serve a number of functions. For example,they may be manually operated by personnel at the remote location toprovide specified signals to personnel at the base station.Alternatively, they may be used in conjunction with apparatus to bemonitored to provide status signals to the base unit. This latterarrangement is illustrated with respect to capacitor 125 which isconnected in series with a solenoid operated switch 127. Switch 127 isin parallel to manually operable switch 126 and is responsive to theoutput derived from a conventional burglar alarm system 128. Occurrenceof an alarm, or fault, condition energizes the output of the burglaralarm 128 to close switch 127. This places capacitor 125 in parallelwith capacitor 100, so that when transistor switch O3 is conductivethere will be produced a unique and identifiable output pulse rate online 16.

By way of example, and to assist in understanding the operation of thebase station monitor networks, it has been found that suitable operationof the remote unit is obtained when oscillator O1 is free running underthe control of capacitor 94 at, for example, 120 cycles per second. Thisfree-running operation occurs when transistor 03 is nonconductive sothat neither the timing capacitor 100 nor the timing transistor 04 canaffect the operation of the oscillator. When O3 is conductive, capacitor100 is provided with a charging path; when it has charged to apredetermined value, it biases transistor 04 on to thereby provide ashunt across capacitor 94 and turn transistor Q1 off. Capacitor 100 thendischarges, causing O4 to become nonconductive, removing the shunt fromcapacitor 94 and allowing 01 again to oscillate until capacitor 100 hasrecharged to the point where 04 again fires. The charging anddischarging of capacitor 100 and the consequent conduction andnonconduction of transistor 04 thus modulates the output of oscillatorQ1, producing a series of output pulses the rate of which will bedependent upon the rate at which capacitor 100 charges and discharges.In a typical example, the value of capacitor 100 may be adjusted toproduce an output pulse rate from oscillator 01 of 1 pulse per second.The operation of any sensor to cut off transistor Q3 will immediatelyreturn oscillator O1 to its free-running state with an output of 120cycles per second and a continuous pulse rate. When capacitor 125, forexample, is connected in parallel with capacitor 100, as by energizationof a burglar alarm, transistor Q4 will be switched between itsconductive and nonconductive states at a rate dependent upon the rate atwhich the two parallel capacitors will charge to the firing voltage ofQ4. By proper selection of the value of capacitor 125, the pulse rate ofthe timing circuit may be reduced from one pulse per second to, forexample, one pulse every 2 seconds. Similarly, the addition of capacitor119 to the timing circuit may further vary the rate of pulse modulationofoscillator Q1.

It will be seen from FIG. 3 that all the power required for theoperation of the remote portion of the present system is derived fromthe direct current applied to lines 14 and 16. Thus, the oscillator 18and its associated amplifier 02 as well as the controller 20 receive allnecessary power from lines 14 and 16. Similarly, the sensors 22, whichin this case are fire detectors or burglar alarms, also derive theirpower from lines 14 and 16, the detectors and 111 being connectedbetween lines 14 and 116, in the manner described above, and burglaralarm 128 being connected between line 14 and 130. Line 130 is connectedby way of terminal 131 to positive line 92 and through amplifier O2 tothe positive supply line 16. It will be noted that sensor 22 isconnected to controller 20 by way of terminals 106, 107, 114, 131, 132and 133, the latter two terminals serving to connect burglar alarmswitch 127 in parallel with the manually operated switch 126. Theseterminals permit connection of various sensors to the controllercircuit. Alternatively, control mechanisms or circuits of various typesmay be connected to the system as will be described hereinbelow.

The output pulses from the oscillator 18 are carried by line 16 to thebase unit illustrated in FIG. 4. These signals are applied by way oftransformer 26 to the input of the first monitor 28. Monitor network 28is a solid-state module which receives input pulses from transformer 26and applies them by way of diode and parallel capacitor 151 to the baseof a first transistor amplifier Q5. The collector of O5 is connected toa positive power supply line 152, while its emitter is connected throughcapacitor 153 to a negative supply, or ground, line 154. The emitter isalso connected to the base of a second transistor amplifier 06 havingits collector connected to line 152 and its emitter connected by way ofline 155 to the other side of the secondary of transformer 26. The greenindicator lamp 30 is connected between line 155 and ground, with aresistor 156 connected in parallel to it to allow the circuits tofunction in the event the bulb burns out. Receipt of a pulse of the 120Hz. signals generated at the remote station at the base of Q5 causes 05to conduct and charge capacitor 153. The current flowing in the emittercircuit of Q5 causes 06 to become conductive. If the pulses received bythe monitor network 28 are at a relatively low rate, as, for example, 1pulse per second, conduction of Q5 and 06 will be intermittent. Thisintermittent output from transistor 06 will be applied by way ofline 155to a timing network made up of series resistors 160 and 161 and shuntcapacitor 162, but will be insufficient to charge capacitor 162. Sinceindicator lamp 30 is in series with the secondary of transformer 26,these intermittent pulses will also cause lamp 30 to lightintermittently, at the same rate as the received pulses. It will benoted that the cascade arrangement of Q5, O6 is made necessary becauseof the use of silicon transistors; other types will not require thisarrangement, but would permit a single transistor to provide the neededswitching and amplifying functions.

The intermittent output of O6 in response to the 1 pulse per secondinput is applied by way of diode 164 and resistor 165 to one side of acapacitor 166, the other side of which is connected to ground. Thisintermittent voltage is sufficient to charge capacitor 166, thusproducing a steady voltage through resistor 167 to the base electrode oftransistor switch ()7. The emitter of O7 is connected to ground line154, while the collector is connected by way of resistor 168 to thepositive supply line 152. As long as Q7 remains conductive, itscollector will be effectively grounded, and no voltage will be appliedto the input of third monitor network 42.

1f the signal pulses applied to transformer 26 vary from the 1 pulse persecond rate, defined as the normal, or ready condition, the status ofthe monitoring networks will be changed from that described above. Ashas been indicated, the ready condition involves the intermittentblinking of green lamp 30, the pulse rating being such as to hold 07conductive to prevent an input to the third monitor 42 and beinginsufficient to charge capacitor 162, thus preventing the second monitorfrom becoming energized. If the pulse length is increased, so that thebase station sees only a continuous, unmodulated, free-running signal of120 cycles per second, for example, transistors Q5 and Q6 will turn on120 times per second. In addition, lamp 330 will blink on 120 times persecond and will thus appear to glow steadily. This increased pulselength will maintain the charge on capacitor 166 and hold transistor 07conductive. In addition, the continuous pulse will provide sufficientvoltage to cause capacitor 162 to become conductive, thus applying avoltage through resistor 161 and across resistor 172 to the baseelectrode of amplifier Q8, the collector of which is connected topositive supply line 152. The emitter of O8 is connected to the baseelectrode of switch Q9, causing it to turn on and close itscollector-emitter path from positive supply line 152, through red lamp34, its collector, its emitter to ground line 154.,Completion of thiscircuit causes red lamp 34 to glow steadily. A resistor 171 is connectedacross lamp 34 to provide continuity of the circuit in the event thelamp should burn out. Thus, the existence of a 120 cycle per secondsignal on line 16 is positively indicated by the glowing of green lamp30 and red lamp34.

A reduction in the pulse rate of the signal appearing on line 16 willalso change the mode of operation of the indicators in FIG. 4. If thepulse rate slows down from the nominal l pulse per second to, forexample, 1 pulseevery 2 seconds, capacitor 162 will be unable to charge,and red lamp 34 will remain off. The green lamp 30 will blink slowly,and while it is turned on, transistor Q6 will be charging capacitor 166to hold Q7 nonconductive. However, the length of time between pulses isso large at this repetition frequency that capacitor 166 will dischargebetween pulses to allow Q7 to become nonconductive. in addition, if afault should occur in the remote unit or in the connecting lines 16 and14 so that no pulses are received at transformer 26, Q7 will also becomenonconductive because of the discharge of 166. Whenever O7 is turnedoff, the voltage appearing across resistor 168 is applied throughresistor 175 to the base of amplifier Q9, causing O9 to conduct. Thecollector of O9 is connected to positive supply line 152 and its emitteris connected to the base of transistor Q10, the emitter of which isconnected to ground. The collector of Q10 is connected through amberindicator lamp 44 to positive supply line 152, and conduction of Q10illuminates lamp 44. Therefore, any state of nonconduction in Q7 resultsin energization of amber lamp 44. 11" it is a low pulse rate (e.g., onepulse every 2 seconds) that is causing O7 to become nonconductive, theresult will be a slow blinking of amber lamp 44. Since, under thiscondition, green lamp 30 is conducting during each pulse and lamp 44 isilluminated during the pause between successive pulses, the result willbe an alternate blinking of the green and amber lights. 11 it isa lossof signal that causes Q7 to be nonconductive, then amber lamp 44 willglow steadily.

It will be apparent, then, that energization of the various lamps in theindicators of FIG. 4 depends upon the pulse rate at which oscillator 18is modulated, and this rate is, in turn, governed by the particulartiming capacitors which are connected in circuit with timing transistorQ4 and thus with the unijunction oscillator transistor 01. Each changein the timing circuit for Q], as represented by capacitors 100, 119 and125, may be identified with a specific event in the apparatus beingmonitored, and thus will produce in the base station a specificindicator light energization which will be a function of the monitoredfunction. For example, when the system is used in conjunction with firedetectors such as those indicated at 110 and 111 in FIG. 3, the properoperation of these detectors, i.e., open circuit between terminals 106and 107, will cause transistor switch 03 to be conductive to placecapacitor 100 in the timing circuit of the oscillator. This will causetransistor 04 to become periodically conductive and nonconductive whichwill, in turn, modulate the oscillator O1 to produce a pulse rate of 1pulse per second, causing the green light 30 to blink and indicatingnormal operation of the fire detector system, If a tire, for example,should short out one of the de tectors, then transistor switch Q3 wouldbecome nonconductive, capacitor 100 would be removed from the timingcircuit and transistor Q1 would oscillate continuously at 120 cycles persecond, causing green lamp 30 to glow steadily and illuminating red lamp34, causing it also to glow steadily to indicate an alarm, or faultcondition. If the first surveillance loop, which includes the negativesupply line in the remote cirwil cuitry, is broken at any point, thatis, if line 14 is broken, the pulse rate becomes zero and the amberlight at the basestation will become illuminated to indicate amalfunction. The second surveillance loop defined by wire 116. isconnected to the base ofQ4 and,'as long as this loop is intact and O3 isconducting, insufficient voltage is applied to O4 to cause it toconduct. However, if supervisory loop 116 is broken, as for example, ifa door or window in a protected area is opened without authorization,the base voltage on 04 will rise sufficiently to cause 04 to conduct.With 04 and Q3 both conducting, the capacitor timing and biasingnetworks of the oscillator are shunted to ground through resistor 112,the oscillator stops producing an output, and the amber light 44 goes onto indicate a malfunction which, in this case, is an alarm condition.If, during the time that surveillance loop 116 is broken, one of thefire detectors 110, 111 should short circuit, the base voltage would beremoved from Q3, opening the shunt to ground through transistor Q4, andthe oscillator would produce a 120 pulse per second output under thecontrol of capacitor 94. This would, of course, produce a steady glow inthe red and green lamps 34 and 30, representing a fire alarm.

In addition to the visual indicators of FIG. 4, the present inventionprovides an audible alarm system which is also responsive to pulse rate,and which is illustrated in FIG. 5. Since a steady glow in red lamp 34is indicative of an active condition, which may be considered an alarmmode, the current through this lamp may be used to operate a switch 36which, in turn, activates a bell 180, a buzzer 181 or their equivalents.During a normal condition, or mode, when only green lamp 30 is blinking,transistor Q9 (FIG. 4) will be nonconductive, permitting a bias voltageto be applied from positive supply line 152 through resistor 171 andline 182 (connected to the collector of 09), through resistor 183 to thebase of transistor 011. The collector of Q11 is connected to positivesupply line 152 through resistor 184, and its emitter is connected toground. In this condition, Q11 is conductive, shunting the voltageacross resistor 184 to ground so that the alarm 38 is not energized.Upon occurrence .of a fire signal or the like which produces a steadyI20 cycle per second signal on line 16 and causes red lamp 34 to light,transistor 09 becomes conductive, shunting the voltage appearing on thebase of 011 to ground and causing Q11 to become nonconductive. Thevoltage across resistor 184 may then be applied through diode 185,switch arm 186 of two-position toggle switch 187, and through resistor188 to the gate electrode of a silicon-controlled rectifier orequivalent solid-state switching device 190. This causes SCR 190 tobecome conductive, completing a current path from positive supply line152 through bell and the anode-cathode path of SCR to ground, therebyenergizing bell 180 to provide the required audible alarm. in responseto this alarm signal, the operator at'the base station may switch toggle187 to the standby position, opening the bell circuit at switch arm 186and silencing the bell. Movement of toggle 187 to standby will place itsother switch arm 194 in contact with terminal 195, switch arms 186 and194 being mechanically connected to operate together and will activatean acknowledgement circuit which functions in the manner known in theart to produce a second alarm when the system has been restored.Terminal 195 is connected through diode 196 to the collector of atransistor switch Q12, the collector of Q12 also being connected throughresistor 197 to positive supply line 152. The Q12 emitter is connectedto negative supply line 154 and its base is connected through diode 198and resistor 199 to the collector of Q1 1. During the time that the redlamp 34 is on and Q11 is nonconductive, the voltage across resistor 184will be applied to the base of Q12, causing Q12 to conduct and shortcircuit the voltage on resistor 197 to ground. Thus, no voltage willappear at the collector of Q12 during that time. When the remotecondition is corrected, so that the monitor networks are no longer intheir active rnode (e.g., a fire alarm signal is no longer being given),the pulse rate will return to 1 pulse per second and the red indicatorlamp will be turned off. The green light will start blinking and 011will become conductive to remove the voltage from the base of O12. O12will stop conducting and a voltage will appear at its collector whichwill be applied through diode 196 and switch arm 194, through resistor200 to the gate electrode of a solid-state switching device such assilicon-controlled rectifier 202. Conduction of SCR 202 will complete acircuit from positive supply line 152 through buzzer 181 and theanode-cathode circuit of SCR 202 to ground, thus sounding the buzzer toprovide an audible indication that the system has returned to normal.The operator at the base station may then return toggle 187 to its onposition, closing the circuit through switch arm 186 to SCR 190 andplacing switch arm 194 in contact with terminal 203, thus placing thealarm circuit again in condition to respond to a fire signal, or othercorresponding active" signal from the remote unit.

If trouble should occur in the connecting lines 14 and 16 or in thesurveillance loop at the remote module so that the amber light is turnedon, the resultant voltage at the collector of Q7 will be applied by wayof line 210 and diode 211 through switch arm 194 to the gate electrodeof SCR 202, causing the buzzer to sound. The voltage on line 210 willalso be applied by way of resistor 212 and diode 213 to the base of 012,causing 012 to become conductive and removing the voltage from itscollector. The operator at the base station may then shift toggle 187 sothat switch arm 194 is in contact with terminal 195, thus silencing thebuzzer. When the trouble has been repaired, the 1 pulse per secondsignal will be returned to the line, and the green dial light 30 willbegin to blink normally. Transistor Q7 will become conductive, removingthe voltage from line 210 and turning off the amber light. 012 returnsto its nonconductive state and restores its collector voltage (whichappears across resistor 197). With switch arm 194 in contact withterminal 195 (standby), this voltage will cause the buzzer to sound,giving audible indication that the system has been returned to normal.Toggle 187 may then be returned to its on condition for normalmonitoring operatron.

The foregoing has indicated the operation of the alarm system inresponse to a fire alarm signal or a trouble signal. lfa burglar alarm,such as that indicated at 128 in FIG. 3, or some equivalent alarm systemis used to switch capacitor 125 into the timing circuit of the modulatorfor oscillator Q1, the resultant output from the remote unit will bereduced in frequency to approximately 1 pulse every 2 seconds, forexample. As has been indicated, this reduced pulse rate will cause thegreen and amber lamps 30 and 44 to blink alternately. Since theintermittent blinking of amber lamp 44 is the result of periodic cuttingoff of transistor 07, it will be apparent that there will becorresponding voltage pulses appearing on line 210 which will be appliedthrough switch arm 194 to cause buzzer 181 to sound intermittently, eachtime the amber light is illuminated. it will be observed that the sametype of signal may be generated at the remote station by the manualclosing of switch 126 in controller 20. This manual switch may thus beconveniently used by a repairman or other personnel located at theremote area for signalling the base station. Similarly, capacitor 119may be connected in the timing circuit of the oscillator by means ofmanually operable switch 121 to produce another pulse rate which may,for example, cause the green and amber lights to blink alternately moreslowly.

Thus, it will be seen that the audible alarm circuit is arranged toprovide an audible response which is indicative of the type of conditionbeing sensed at the remote unit. The audible alarm may be switched tostandby while the remote condition is being corrected, and whencorrection has been accomplished the audible alarm will again sound toindicate a return to normal. The alarm circuit consists of two alarms,the first being responsive to the second (red) monitor network, and thesecond being responsive to the third (amber) monitor network. The secondalarm has a standby position to provide an acknowledgement circuit whichserves to indicate when the condition which excited the second or thirdmonitor networks has been corrected, and the base system is to be reset.

In addition to the general surveillance functions described above, thepresent system is readily adapted to the remote control of machineoperations, permitting remote turning on of machinery, monitoring of itsoperation and emergency shutdown. In addition, the system willaccommodate superimposed signals representing flow measurements such asthe flow of gas, oil, water or other fluids, stress measurements,measurement of airflow velocity, such as in a coal mine ventilationsystem, and the like.

Monitoring of machine operation is accomplished preferably through thedetection of machinery motion such as rotation or reciprocation.Malfunction of the machine would cause a change in the indicator lightswith accompanying audible alarms. By switching the alarm system tostandby, the operator at the base station may check the continuity ofthe control system, and if it is indicated as operating properly, theoperator will know that the malfunction is elsewhere. When the machineis restored to normal operation, the audible alarm will again sound andthe base station is again returned to its normal operating condition.Thus, the operator at the base station can at all times determinewhether he has a clear con trol and monitoring circuit to the remotelylocated machinery.

Turning now to FIG. 6, a modified form of sensor 22 particularlydesigned for machine control and monitoring is illustrated. With thissystem, the power control module 60 (FIG. 2) would be used so that whenresistors 62, 64 and 66 are in series with the DC supply lines 14 and16, a slightly reduced voltage is provided. Closure of on-off switch 70shunts resistor 66 to raise the positive supply voltage on line 16,which is illustrated as the 13+ line in FIG. 6. This increased voltageis applied through a resistor 220 and diode 221 to the gate electrode ofa suitable solid-state switching device such as a silicon-controlledrectifier 222. The increased voltage causes the SCR 222 to conduct,completing a machine power loop 224 which includes the secondary of anAC power supply transforrner 226, coil 227 of a switch relay 228, theanode-cathode circuit of SCR 222, ground return line 229 and diode 230.Conduction of SCR 222 thus energizes switch relay 228 to close switcharm 231 and energize the machine 232 to be controlled and monitored.

Energization of machine 232 will produce a motion which may be detectedby the sensor circuit 22. As illustrated in FIG. 6, a magnetic reedcircuit is utilized in conjunction with a moving permanent magnet toproduce the required sensing. A permanent magnet 240 is mounted on arotating or reciprocating portion of machine 232 and is arranged to passin sequence first past magnet reed switch 241 and then past reed switch242. As the magnet nears reed switch 241, its contacts 243 close,completing a circuit from positive supply line 16 through resistor 244,contacts 243, resistor 245 and storage capacitor 246 to negative supplyline 14. During the time that contacts 243 are closed, a charge buildsup on storage capacitor 246. As the magnet moves away from switch 241,contacts 243 open, the stored voltage remaining on capacitor 246.Movement of magnet 240 toward reed switch 242 causes contacts 247 toclose, forming a discharge path for capacitor 246 through the closedcontacts 247 to a second storage capacitor 248. The storage of a voltageon capacitor 248 applies a bias through resistor 249 to the base oftransistor switch Q13, causing it to conduct. The emitter of Q13 isconnected to ground line 14, while its collector is connected by way ofterminal 106 to the base of transistor Q3 in the control network of FIG.3. At the same time, this voltage is applied by way of terminal 114 tothe base of transistor 04. This voltage causes transistor 04 to conduct,but conduction of Q13 short circuits the base bias on transistor Q3 andswitches it to its nonconductive state, thus opening the emittercollector circuit of Q4 and leaving capacitor 94 to control thefrequency of oscillator 01. As has been explained, with only capacitor94 in circuit with oscillator Q1, the oscillator is free running atcycles per second, a frequency which causes both the green and the redlamps 30 and 34 at the base station to glow continuously. Thus, with theproper timing of the operation of reed switches 241 and 242, indicatorlamps 30 and 34 are caused to glow, giving a positive indication of anactive status at the remote station, and thus of proper machineoperation.

if the machine malfunctions in some way, so that the motion of magnet240 varies from the sequence which maintains Q13 in a conductive state,or if the machine stops entirely so that no voltage is applied acrossstorage capacitor 248, this capacitor will discharge, returning Q13 toits nonconductive condition and shifting Q3 to a conductive state. Thiswill connect the oscillator modulating network consisting of capacitor100 and transistor O4 in parallel with capacitor 94, thereby causing theoscillator to be pulse modulated and changing the output of the remoteunit to l pulseper second. As before, this will shift the indicatorlights at the base stations so that the green lamp 30 pulsesintermittently and the red light will be turned off. The pulsing greenlight indicates a ready condition; i.e., that the control and sensingcircuitry is operating properly and that the malfunction has occurred inthe machine itself. The operator at the base station may then shut downthe machine by opening switch 70 (FIG. 2).

The alarm system for use with the machine control system of FIG. 6differs from the alarm circuit described in FIG. 5. This modified alarmcircuit is illustrated in FIG. 7, to which reference will now be made.As in FIG. embodiment, the alarm circuit of HG. 7 utilizes switch 36 andits corresponding transistor Q11 for response to the condition of thesecond monitor network and red indicator lamp 34. When lamp 34 isglowing, indicating proper operation of the machine being monitored, novoltage is applied to the base of transistor Q11 and this lattertransistor is nonconductive. This permits the voltage appearing acrossresistor 184 to be applied through diode 270 to the standby terminal 271of toggle switch 272. The voltage across 184 is also applied by way ofresistor 273 and diode 274 to the base electrode of transistor switchQ14, the emitter of which is connected to ground line 154 and thecollector of which is connected through resistor 275 to the positivesupply line 152. The voltage thus applied to the base of 014 makes thistransistor conductive, dropping its collector voltage to ground level.This is the operating condition for this circuit which remains until thered lamp goes off. When this happens, Q11 becomes conductive, removingthe bias voltage from the base of Q14 and turning Q14 ofi. The voltagewhich then appears at the collector of 014 is applied through diode 276to the on terminal 277 of toggle switch 272 and thence through resistor278 to the gate electrode of a silicon-com.

trolled rectifier 280. This causes rectifier 280 to become conductiv e,closing a circuit from positive supply line 152 through buzzer 281 andSCR 280 to line 154, thus sounding the buzzer. The operator at the basestation may then shift switch arm 272 to the standby position until arepair of the remotely located machine is effected. When this happens,the red light goes on, Q11 stops conducting and the voltage acrossresistor 184 is applied through switch arm 272 to the SCR 280, soundingthe buzzer. The operator may then shift the switch arm to the oncondition, restoring the circuit to its normal condition.

If, upon occurrence of a malfunction in the machine, the operator at thebase station opens switch 70 to turn off the machine, buzzer 281 willnot be able to respond to repair of the malfunction automatically; i.e.,the machine will not run, so red lamp 34 will not light. Therefore, themanually operable switches 121 and 126 which permit connection ofcapacitors 1 19 and 125, respectively, into the timing circuit ofoscillator Q1 are particularly useful in this embodiment, for theypermit a repairman at the remote area to send a signal to the baselocation by switching capacitors 119 or 125 into the circuit. Aspreviously indicated, capacitors 125 may produce a pulse rate which willcausethe green and amber lamps to blink alternately. Capacitor 119 maybe selected to have a value which will produce the lowest rate of pulsemodulation of the unijunction transistor oscillator. This capacitor maybe selected so as to produce relatively long pulses, widely spaced. Whenthis capacitor is inserted in the circuit by closing switch 121, therelatively long pulse will cause the green lamp to turn on and then the.red lamp to turn on briefly. The space between succeeding pulses againwill cause the amber lamp to light, thus producing a green-red-am.bersequence of blinking lights. This sequence of operation will causebuzzer 281 to sound intermittently when switching 272 is in the standbyposition. The intermittent blinking of all three lights might be used bypersonnel at the remote location to signal the base station to start themachinery by closing switch 70. If this is done, normal lightindications of machinery operation will override the serviceindications. if the repair personnel desire to shut down the equipmentat the remote location, switch 126 might be used to indicate byalternately blinking green and amber lamps that the machine has beenshutdown on purpose. Upon receipt of such a signal, the operator at thebase location would place switch 272 in standby, so that when themachine is restored to normal operation at the remote location, thebuzzer will sound to warn'that the system is again active, and the greenand red lamps will go on.

It will be seen that if the machinery, once placed in operation, ceasesto operate properly because of a malfunction in the machine, the redindicator lamp 34 will be extinguished and an audible buzzerwill sound.The operator at the base station would then change switch 272 to itsstandby position and, if green lamp starts blinking, the operator isassured that the entire control system to the remote area is functioningproperly. if the green and red indicators are both out, the amber lampwill light, indicating a malfunction in the control circuitry.

Although the circuit of FiG. 6 is described with reference to Y themotion of a machine, it will be apparent that this sensor ble detectorwhich, upon occurrence of a malfunction will cut off transistor Q13, orotherwise open the circuit between terminals 106 and 107 formed throughthe collector-emitter circuit ofQl3 may be used with this system.

It will be apparent that numerous modules, both remote and base, can beused in conjunction with a single installation, with various modulesbeing used to measure or detect specific functions of the installation.One example of a suitable application for this type of module is inconjunction with conveyors used in coal mines, where one of the problemsencountered is the use of four or more conveyors converging into acommon carrier, Such an arrangement can create overloading. To avoidthis, weight limiting switches can be connected across terminals 106 and107 and when the limiting switch of any one of the conveyors closesbecause of an overload condition the operator at the base station willimmediately receive a suitable warning signal, enabling him to shut downthe overloaded conveyor from the remote location. Since the remotemodules require no local power source, transferring of the conveyorsystems from one location to another poses no particular problemsinsofar as the telemetry is concerned.

Signals may be superimposed on line 16 connecting the remote unit to thebase unit through the use of a probe amplifier 72 (FIG. 2). This probeis shown in detail in FlG..8 and comprises a variable resistance device300 of any suitable type. The nature of variable resistor 300 willdepend upon the parameters to be measured by the probe, but typicallythe resistive device may be a photocell or a thermistor. Variableresistor 300 may be connected by way of switch 301 across a resistor 302connected in line 16. Capacitor 303 may be connected in parallel withresistor 302. Variations in resistor 300 will thus produce a slightvariation in the current carried by line 16, which variations may bedetected by meter amplifier 74 (P16. 2). If desired, the effect ofchanges in resistor 300 may be enhanced through the use of transistoramplifier 015 by changing switch 301 to the base of 015.

FIG. 9 illustrates a suitable meter amplifier 74 which may be connectedin line 16 to sense changes in the line current effected by probeamplifier 72. This amplifier may detect 2 or 3 volt changes caused bythe probe amplifier and register these changes on meter 310. Apotentiometer 311 is connected in series with line 16, with the slidearm of the potentiometer being connected to the base of amplifier Q16,whereby voltage changes in line 16 may be detected. Potentiometers 312and 313 connected across Zener diode 314 and between the positive andnegative supply lines indicated at 8+ and 8- provide calibration formeter 310. where the meter amplifier is used in conjunction with thepower supply switch 60, the opening of switch 70 to shut down a remotemachine places resistor 66 in the line and this will produce asufficient voltage drop in the line to make the meter amplifier 74inactive; that is, insufficient voltage will be applied to the base of016 to make it conductive.

Thus, there has been described a system for monitoring and controllingremote apparatus or installations. The system is capable of sensing agreat variety of activities, such as fire detection systems, burglaralarms, machine operation, fluid flow, and the like and providing aunique indication at a base station of the status of the system beingmonitored. Various combinations of indicator lamps illustrate theparticular mode in which the remote system is operating in response tothe condition being sensed, and audible alarm signals may be provided asfurther warning of abnormal conditions. The audible alarm system mayalso be provided with a standby mode so that when malfunctions in theremote unit are repaired, a positive indication of such repair is givenat the base unit so that the system can be returned to its normalcondition. in addition, unique signaling means are provided which may,in some embodiments, be used to provide further monitoring inputs and,in other embodiments may be used as manual signalling devices to permitcommunication between personnel located at the remote location and atthe base location. Although the present invention has been describedwith respect to particular embodiments, it will be apparent to thoseskilled in the art that numerous variations and modifications can bemade in the circuits shown and described without departing from the truespirit and scope of the present invention. Therefore, it is desired thatthe present invention be taken as illustrative, and that the scope andextent of the invention be limited only by the following claims.

lclaim:

l. A system for monitoring at a base location the pulse rate of signalsgenerated at and transmitted from a remote location, comprising:

a remote station including an oscillator for generating said signals,means connected to said oscillator for establishing a frequency ofoperation of said oscillator and thus the frequency of said signal, acontroller circuit for said oscillator, said controller circuitcomprising means for modulating said oscillator to produce saidfrequency signals at a first pulse rate, and sensor means responsive toselected conditions at said remote station, said modulating means beingresponsive to said sensor means to change the pulse rate of saidfrequency signals whereby said pulse rate is indicative of a sensedcondition;

means for transmitting said signals; and

a base station for receiving said signals, said base station includingfirst indicator means responsive to the pulse rate of said signals forproviding an indication of the condition being sensed, second indicatormeans including first charge storage means connected to, and responsiveto the operation of said first indicator means, the operation of saidsecond indicator means being determined by the accumulated charge onsaid first charge storage means whereby both said indicator meansprovide an indication of said sensed condition.

2. The system of claim 1, wherein said means for modulating saidoscillator includes a timing capacitor connected in circuit with saidoscillator, and wherein said controller circuit further includes atleast one control capacitor connectable in circuit with saidtiming'capacitor.

3. The system of claim 2, wherein said sensor circuit includes switchmeans responsive to a selected condition for connecting said controlcapacitor in parallel with said timing capacitor.

4. The system of claim 1, wherein said means for transmitting saidsignals comprises first and second lines extending from said remotestation to said base station, said system further including power supplymeans at said base location and connected to said remote station by wayof said first and second lines to provide the sole source of electricalpower to said remote station, said power supply being electricallyisolated from said base station.

5. The system of claim 4, further including power control means at saidbase location and in circuit with said power supply means, and switchmeans at said remote station responsive to said power control means foreffecting a selected control function at said remote location, saidsensor means being responsive to the condition of said selected controlfunction.

6. The system of claim 1, further including third indicator meansincluding second charge storage means connected to, and responsive tothe operation of, said first indicator means, the accumulated charge onsaid second charge storage means determining the operation of said thirdindicator means, whereby all three indicator means cooperate to providea unique indication for each sensed condition.

7, The system of claim 6, said base station further including an audiblealarm circuit having an on mode and a standby mode, said alarm circuitbeing connected to said second and third indicator means and responsiveto selected sensed condi' tions.

8. The system of claim 6, wherein said base station includes means forapplying received signals to said first indicator means, said firstindicator means responding to signals having said first pulse rate, andsaid second and third indicator means being nonresponsive to signalshaving said first pulse rate, thereby providing a first mode indication,said first indicator means responding to a second pulse rate to chargesaid first charge storage means, whereby said second indicator meansresponds but said third indicator means remains nonresponsive to signalshaving said second pulse rate, thereby providing a second modeindication, said first indicator means responding to signals having athird pulse rate to permit said second charge storage means to chargeand discharge intennittently, whereby said first and third indicatormeans respond alternately and said second indicator means remainsnonresponsive to provide a third mode indication, said first indicatormeans responding to signals having a fourth pulse rate to charge saidfirst and second charge storage means and thereafter to permit saidsecond charge storage means to discharge, .whereby said first, secondand third indicator means respond sequentially to provide a fourth modeindication, and said first indicator means being nonresponsive tosignals having a fifth pulse rate to permit said second charge storagemeans to discharge, whereby only said third indicator means responds toprovide a fifth mode indication.

9. The system of claim 8 wherein said base station further includes anaudible alarm circuit having first and second alarms, said alarm circuitbeing connected to said second and third indicating means and having anon mode wherein said first alarm is energized whenever said secondindicator means responds to said received signals and said second alarmis energized whenever said third indicator means responds to saidreceived signals, said alarm circuit having a standby mode wherein saidsecond alarm is energized when said second or third indicator meansreturns to a nonresponsive condition.

10. The system of claim 6, wherein said first indicator means includes afirst visual indicator responsive to and indicative to the pulse rate ofsaid received signals.

11. The system of claim 10, wherein said second indicator means includesa timing network and a second visual indicator responsive to the outputof said timing network, said timing network limiting the response ofsaid second visual indicator to selected pulse rates.

12. The system of claim 11, wherein said third indicator means includesa third visual indicator, said system further including a second timingnetwork and a monitor switch connected between said first and said thirdindicator means for limiting the response of said third visual indicatorto selected pulse rates.

13. The system of claim 12, further including an alarm circuit connectedto said second and third indicator means and having an on mode and astandby mode, said alarm circuit having first and second alarmsresponsive to selected pulse rates.

14. The system of claim 13, wherein said alarm circuit is connected toand responsive to the state of energization of said second and thirdvisual indicators.

15. The system of claim 1, wherein said controller circuit means formodulating said oscillator comprises a timing capacitor and a timingswitch means responsive to the charge on said timing capacitor forperiodically shunting said timing capacitor and said means forestablishing the frequency of said oscillator thereby periodically tointerrupt the oscillation of said oscillator and establish said firstpulse rate.

16. The system of claim 15, wherein said timing switch means forshunting said timing capacitor comprises a first control transistor,said controller circuit further including a second control transistor inseries with said timing capacitor, said first and second controltransistors comprising switch means operable in response to said sensormeans for controlling the modulation of said oscillator.

17. The system of claim 16, said controller circuit further including atleast one control capacitor and a corresponding control switch means,said control switch means being operable to connect said correspondingcontrol capacitor in parallel with said timing capacitor, the connectionof said control capacitor varying said means for modulating saidoscillator to produce a unique pulse output rate.

18. The system of claim 17, wherein said sensor means comprises aplurality of sensor units, each said sensor unit being connected tooperate one of said switch means.

19. The system of claim 17, wherein at least one of said switch means ismanually operated.

20. The system of claim 15, wherein said sensor means comprises at leastone surveillance loop.

21. The system of claim 15, wherein said sensor means comprises firedetector means.

22. The system of claim 15, wherein said sensor means comprises amotion-sensing device.

23. The system of claim 22, wherein said motion-sensing device includesa first reed switch and first storage capacitor and a second reed switchand second storage capacitor, means for closing said reed switchessequentially to thereby charge said storage capacitors sequentially, thecharge on said second storage capacitor serving to operate said switchmeans for varying said timing capacitor.

24. The system of claim 16, wherein said oscillator means includes aunijunction transistor having an emitter electrode and two baseelectrodes, said means for establishing the frequency of operation ofsaid oscillator comprising a biasing capacitor 'connected to saidemitter electrode, the charging rate of said biasing capacitorregulating said frequency of operation.

1. A system for monitoring at a base location the pulse rate of signalsgenerated at and transmitted from a remote location, comprising: aremote station including an oscillator for generating said signals,means connected to said oscillator for establishing a frequency ofoperation of said oscillator and thus the frequency of said signal, acontroller circuit for said oscillator, said controller circuitcomprising means for modulating said oscillator to produce saidfrequency signals at a first pulse rate, and sensor means responsive toselected conditions at said remote station, said modulating means beingresponsive to said sensor means to change the pulse rate of saidfrequency signals whereby said pulse rate is indicative of a sensedcondition; means for transmitting said signals; and a base station forreceiving said signals, said base station including first indicatormeans responsive to the pulse rate of said signals for providing anindication of the condition being sensed, second indicator meansincluding first charge storage means connected to, and responsive to theoperation of said first indicator means, the operation of said secondindicator means being determined by the accumulated charge on said firstcharge storage means whereby both said indicator means provide anindication of said sensed condition.
 2. The system of claim 1, whereinsaid means for modulating said oscillator includes a timing capacitorconnected in circuit with said oscillator, and wherein said controllercircuit further includes at least one control capacitor connectable incircuit with said timing capacitor.
 3. The system of claim 2, whereinsaid sensor circuit includes switch means responsive to a selectedcondition for connecting said control capacitor in parallel with saidtiming capacitor.
 4. The system of claim 1, wherein said means fortransmitting said signals comprises first and second lines extendingfrom said remote station to said base station, said system furtherincluding power supply means at said base location and connected to saidremote station by way of said first and second lines to provide the solesource of electrical power to said remote station, said power supplybeing electrically isolated from said base station.
 5. The system ofclaim 4, further including power control means at said base location andin circuit with said power supply means, and switch means at said remotestation responsive to said power control means for effecting a selectedcontrol function at said remote locatiOn, said sensor means beingresponsive to the condition of said selected control function.
 6. Thesystem of claim 1, further including third indicator means includingsecond charge storage means connected to, and responsive to theoperation of, said first indicator means, the accumulated charge on saidsecond charge storage means determining the operation of said thirdindicator means, whereby all three indicator means cooperate to providea unique indication for each sensed condition. 7, The system of claim 6,said base station further including an audible alarm circuit having anon mode and a standby mode, said alarm circuit being connected to saidsecond and third indicator means and responsive to selected sensedconditions.
 8. The system of claim 6, wherein said base station includesmeans for applying received signals to said first indicator means, saidfirst indicator means responding to signals having said first pulserate, and said second and third indicator means being nonresponsive tosignals having said first pulse rate, thereby providing a first modeindication, said first indicator means responding to a second pulse rateto charge said first charge storage means, whereby said second indicatormeans responds but said third indicator means remains nonresponsive tosignals having said second pulse rate, thereby providing a second modeindication, said first indicator means responding to signals having athird pulse rate to permit said second charge storage means to chargeand discharge intermittently, whereby said first and third indicatormeans respond alternately and said second indicator means remainsnonresponsive to provide a third mode indication, said first indicatormeans responding to signals having a fourth pulse rate to charge saidfirst and second charge storage means and thereafter to permit saidsecond charge storage means to discharge, whereby said first, second andthird indicator means respond sequentially to provide a fourth modeindication, and said first indicator means being nonresponsive tosignals having a fifth pulse rate to permit said second charge storagemeans to discharge, whereby only said third indicator means responds toprovide a fifth mode indication.
 9. The system of claim 8 wherein saidbase station further includes an audible alarm circuit having first andsecond alarms, said alarm circuit being connected to said second andthird indicating means and having an on mode wherein said first alarm isenergized whenever said second indicator means responds to said receivedsignals and said second alarm is energized whenever said third indicatormeans responds to said received signals, said alarm circuit having astandby mode wherein said second alarm is energized when said second orthird indicator means returns to a nonresponsive condition.
 10. Thesystem of claim 6, wherein said first indicator means includes a firstvisual indicator responsive to and indicative to the pulse rate of saidreceived signals.
 11. The system of claim 10, wherein said secondindicator means includes a timing network and a second visual indicatorresponsive to the output of said timing network, said timing networklimiting the response of said second visual indicator to selected pulserates.
 12. The system of claim 11, wherein said third indicator meansincludes a third visual indicator, said system further including asecond timing network and a monitor switch connected between said firstand said third indicator means for limiting the response of said thirdvisual indicator to selected pulse rates.
 13. The system of claim 12,further including an alarm circuit connected to said second and thirdindicator means and having an on mode and a standby mode, said alarmcircuit having first and second alarms responsive to selected pulserates.
 14. The system of claim 13, wherein said alarm circuit isconnected to and responsive to the state of energization of said secondand third visual indicators.
 15. The system of claim 1, whereiN saidcontroller circuit means for modulating said oscillator comprises atiming capacitor and a timing switch means responsive to the charge onsaid timing capacitor for periodically shunting said timing capacitorand said means for establishing the frequency of said oscillator therebyperiodically to interrupt the oscillation of said oscillator andestablish said first pulse rate.
 16. The system of claim 15, whereinsaid timing switch means for shunting said timing capacitor comprises afirst control transistor, said controller circuit further including asecond control transistor in series with said timing capacitor, saidfirst and second control transistors comprising switch means operable inresponse to said sensor means for controlling the modulation of saidoscillator.
 17. The system of claim 16, said controller circuit furtherincluding at least one control capacitor and a corresponding controlswitch means, said control switch means being operable to connect saidcorresponding control capacitor in parallel with said timing capacitor,the connection of said control capacitor varying said means formodulating said oscillator to produce a unique pulse output rate. 18.The system of claim 17, wherein said sensor means comprises a pluralityof sensor units, each said sensor unit being connected to operate one ofsaid switch means.
 19. The system of claim 17, wherein at least one ofsaid switch means is manually operated.
 20. The system of claim 15,wherein said sensor means comprises at least one surveillance loop. 21.The system of claim 15, wherein said sensor means comprises firedetector means.
 22. The system of claim 15, wherein said sensor meanscomprises a motion-sensing device.
 23. The system of claim 22, whereinsaid motion-sensing device includes a first reed switch and firststorage capacitor and a second reed switch and second storage capacitor,means for closing said reed switches sequentially to thereby charge saidstorage capacitors sequentially, the charge on said second storagecapacitor serving to operate said switch means for varying said timingcapacitor.
 24. The system of claim 16, wherein said oscillator meansincludes a unijunction transistor having an emitter electrode and twobase electrodes, said means for establishing the frequency of operationof said oscillator comprising a biasing capacitor connected to saidemitter electrode, the charging rate of said biasing capacitorregulating said frequency of operation.